Continuously variable ratio transmission system

ABSTRACT

A multi-regime continuously variable ratio transmission system has coaxial system input and output shafts ( 16, 24 ), a continously variable ratio transmission unit (V) connected coaxially to the system input shaft ( 16 ) and having a coaxial variator output shaft ( 18 ) and a mixing epicyclic gear train (E 1 ) having an input sun gear (S 1 ) drivably connected to the variator ouput shaft ( 18 ), a planet carrier (C 1 ) drivably connected to the system input shaft ( 16 ) and a planet gear (P 1 ) mounted on the planet carrier ((C 1 ). The planet gear (P 1 ) drives a first intermediate output shaft ( 22 ) arranged coaxially with the system input shaft ( 16 ) and selectively connectable to the system output shaft via a first clutch (H) in high-regime operation of the transmission. The planet gear (P 1 ) also provides the input for a second epicyclic gear train (E 2 ) having an output (C 2 ) which is selectively connectable to the system output shaft via a braking element (L) for low-regime operation of the transmission. The arrangement minimises the number of gear meshes, thereby minimising transmission losses and the absence of an annulus in the mixing epicyclic gear train (E 1 ) allows more freedom in the choice of gear sizes, thereby permitting reduced gear speeds.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to continuously variable ratiotransmission systems.

It is known to provide a continuously variable ratio transmission systemhaving coaxial system input and output shaft and a continuously variableratio transmission unit (known as a variator) connected coaxially to thesystem input shaft and having a coaxial variator output shaft. A mixingepicyclic gear train receives drives from the system input and from thevariator output. By appropriate use of clutches or other brakingelements, the system can operate in a high-gearing regime or low-gearingregime. Examples of such transmissions can be found in JP-A-6-174033 andJP-A-62-255655.

2. Background Art

Inevitably, small power losses arise from the intermeshing of gears. Inorder to maximise efficiency, it is therefore desirable to reduce thenumber of gear meshes, particularly in the mixing epicyclic gear trainwhere the losses can effectively be magnified during operation in a“power recirculation” mode. It is thus an object of the presentinvention to provide a “coaxial” continuously variable ratiotransmission of the type described with a reduced number of gear meshes.

The prior art “coaxial” arrangements also require relatively high gearspeeds which in turn demand more expensive bearings and tend to increasewear. It is an object of the present invention to reduce such gearspeeds.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided amulti-regime, continuously variable ratio transmission system,comprising:

coaxial system input and output shafts;

a continuously variable ratio transmission unit (variator) connectedcoaxially to the system input shaft and having a coaxial variator outputshaft; and

a mixing epicyclic gear train having an input sun gear drivablyconnected to the variator output shaft, a planet carrier drivablyconnected to the system input shaft and a first planet gear mounted onthe planet carrier and drivingly engaged with the input sun gear;

characterised in that the first planet gear drives a first intermediateoutput shaft which is arranged coaxially with the system input shaft andwhich is selectively connectable to the system output shaft via a firstclutch in a high-regime operation of the transmission;

and in that the first planet gear provides the input for a secondepicyclic gear train having an output which is selectively connectableto the system output shaft via a braking element in a low-regimeoperation of the transmission.

With the above arrangement, when the output of the second epicyclic geartrain is connected to the system output shaft (which corresponds tolow-regime operation) the number of meshing gears can be minimised,thereby minimising the losses which occur in the mixing epicyclic geartrain, particularly when in a power recirculation mode. Moreover, themixing epicyclic gear train of the above arrangement does not require anannulus or ring gear. This significantly reduces the physical sizerequired for the mixing epicyclic gear set and, as a consequence, allowsmuch greater flexibility with the selection of the relative sizes of theplanet gear and planet carrier. The arrangement allows the selection ofgears which permit the mixing epicyclic gear train to run at slowerspeeds as compared with the prior art arrangements, thereby reducingwear, minimising losses and reducing the demand on other components suchas bearings.

The above arrangement also allows power recirculation to take place inhigh-regime operation of the transmission.

Preferably, the first intermediate output shaft is provided with a sungear which is driven by the first planet carrier of the mixing epicyclicgear train. Preferably, the sun gear on the output shaft is the samesize as the input sun gear.

The axle of the planet gear of the mixing epicyclic gear trainpreferably carries a second planet gear which rotates with the firstplanet gear and drives the first intermediate output shaft.Conveniently, the second planet gear is the same size as the firstplanet gear.

The axle of the first planet gear of the mixing epicyclic gear train maycarry a third planet gear which rotates with the first planet gear andprovides the input for the second epicyclic gear train.

The second epicyclic gear train preferably comprises a second input sungear driven by the mixing epicyclic gear train, a planet gear driven bythe second input sun gear and a planet carrier forming the output of thesecond epicyclic gear train.

Preferably the system further comprises intermediate gearing furtherconnecting the mixing epicyclic gear train and the second input sungear.

Preferably, the second epicyclic gear train comprises a second sun gearengaged with the planet gear of the second epicyclic gear train.

In one embodiment, the system comprises means for selectively brakingthe second sun gear. This may conveniently comprise a clutch interposedbetween the second sun gear and the transmission system casing.

In another embodiment, the sun gear is held stationary with respect tothe transmission casing and the braking element comprises clutch meansfor selectively connecting the output of the second epicyclic gear trainto the system output shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, specific embodiments of the present inventionwill now be described, with reference to the accompanying drawings, inwhich:

FIG. 1 is a diagrammatic illustration of a first embodiment ofcontinuously variable transmission in accordance with the presentinvention; and

FIG. 2 is a diagrammatic illustration of a second embodiment ofcontinuously variable transmission in accordance with the presentinvention, as a modification of the embodiment of FIG. 1.

Referring firstly to FIG. 1, a continuously variable ratio transmissionsystem comprises a variator V of the known toroidal race rollingtraction type having two toroidally-recessed discs 10 arranged one ateach end of the unit and a pair of similar output discs 12, each facinga respective one of the input discs 10 and rotating with each other.Sets of rollers 14 are mounted between the opposing faces of the inputand output discs 10, 12 to transmit drive from the input discs 10 to theoutput discs 12 with a ratio which is variable by tilting the rollers14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIENT(S)

The input discs 10 are connected to and driven by a system input shaft16. The variator provides an output via a tubular variator output shaft18 which is arranged coaxially with the input shaft 16. The end of theshaft 18 remote from the variator V drives the sun gear S1 of a first,mixing epicyclic gear train E1. The carrier C1 of the gear train E1 isconnected to, and driven by, the input shaft 16 and is also connected tothe inner of the two variator input discs 10. The carrier C1 carriesinput planet gears P1 which engage with, and are driven by, the sun gearS1. The planet gears P1 are each mounted on the carrier C1 by means ofan associated shaft 20 which additionally carries first and secondoutput planet gears PX1 and PY1. Output planet gear PX1 is identical toplanet gear P1 and transfers the summed output of the gear train E1 viaan output sun gear S2 (of the same size as input sun gear S1) to anintermediate output shaft 22 arranged coaxially with the system inputshaft 16. Drive from the intermediate output shaft can be selectivelytransmitted via a high-regime clutch H to a system output shaft 24.

Output planet gear PY1 is of smaller diameter than planet gears P1 andPX1 and meshes with a pinion 26 formed on one end of a tubularintermediate output shaft 28 arranged coaxially with the input shaft 16.The opposite end of the intermediate output shaft is also provided witha pinion 30 of smaller diameter than pinion 26. The pinion 30 mesheswith larger diameter planet gears P2 of a second, simple reversingepicyclic gear set D2. The planet gears P2 are mounted on a carrier C2which is connected to a second tubular intermediate output shaft 32arranged coaxially with the system input shaft 16, and which in turn isconnected to the system output shaft 24.

The planet gears P2 of the second epicyclic gear set E2 are each locatedat one end of a respective shaft 34 mounted in the carrier C2. Theopposite end of each shaft 34 carries a further, smaller planet gear PX2which mesh with a sun gear 36 located at one end of a tubular transfershaft 38 arranged coaxially with the system input shaft 16. The otherend of the transfer shaft 38 is connected to one side of a brakingelement in the form of a low-regime clutch L, the other side of which isconnected to the transmission casing 40.

The transmission can operate in one of three regimes, namely highregime, low regime and synchronous mode.

In high regime, in which the transmission operates at ratios fromsynchronous mode ratio to deep overdrive, the high regime clutch H isengaged and the low regime clutch L is disengaged. This allows theoutput of the mixing epicyclic gear set E1, which receives inputs fromboth the input discs 10 and the output discs 12 of the variator V, to betransmitted to the system output shaft 24 from output planet gears PX1of the first epicyclic gear set E1, the output sun gear S2, theintermediate output shaft 22 and the high regime clutch H. An outputfrom the other output planet gears PY1 of the first mixing epicyclicgear set E1 is also transmitted to the second epicyclic gear set E2, butsince the low regime clutch L is disengaged, the output is nottransmitted to the carrier C2 and indeed the carrier C2 merely rotateswith the system output shaft 24 to which it is connected. If sun gearsS1 and S2 are of the same diameter, the intermediate shaft 22 willrotate at the same speed as the variator output shaft 18. Howevervarying the relative sizes of gears S1 and S2 will create a secondepicyclic functioning much as the low regime gear train. Consequentlythe arrangement simply allows power recirculation to take place via thevariator V in high-regime operation. The synchronous shift point canthen be determined independently of the ratio spread of the variator.

In low regime, in which the transmission operates from full reverse,through “geared neutral” to synchronous mode ratio, the high regimeclutch H is disengaged and the low regime clutch L is engaged.Disengagement of the high regime clutch H isolates the system outputshaft 24 from the output planet gear PX1 of the mixing epicyclic gearset E1. Furthermore, engagement of the low regime clutch L allows theoutput drive from the first mixing epicyclic gear set E1 to the secondepicyclic gear set E2 to be transferred to the carrier C2 of the secondepicyclic gear set E2 by providing a reaction force from thetransmission casing 40. The drive is then transmitted to the secondtubular intermediate output shaft 32 and thence to the system outputshaft 24.

Moving from high regime to low regime or vice versa can be achieved inso-called “synchronous mode” in which the transmission operates in acondition in which the intermediate output shaft 22 leading from themixing epicyclic gear set E1 and the second tubular intermediate outputshaft 32 leading from the second epicyclic gear set E2 rotate at (orvery near) the same speed. In order to change regime, the clutch of thenew regime is engaged, whereby both clutches are simultaneously engagedfor a short time and the clutch of the old regime is then disengaged.

It will be observed that in low-regime, the only gears which areactively engaged in the mixing epicyclic gear set E1 are the planetarygears P1 and PY1, thereby minimising the losses which occur in themixing epicyclic gear train E1, particularly in power recirculationmode. In high regime operation, there are no more meshes than prior arttransmissions. However, it should also be noted that the presentinvention allows the use of a mixing epicyclic gear set E1 which doesnot have an annulus or ring gear. Not only does this reduce the weightof the transmission, but it also allows greater flexibility with theselection of the relative sizes of planetary gears P1, PX1 and PY1. Thisin turn allows the speed of the components to be reduced and reduces thenumber of meshes to a minimum.

The embodiment of FIG. 2 is very similar to that of FIG. 1, the onlysignificant difference being the location of the low-regime brakingmember. Features of the FIG. 2 embodiment which correspond to featuresof the FIG. 1 embodiment are indicated by the same reference numeralsand only the differences in construction will be described.

The differences relate to the second epicyclic gear set, identified asE2′ in FIG. 2. The planet gears P2 and PX2 are identical to those of thefirst embodiment but the sun gear 36′ is fixedly connected to thetransmission casing 40. Drive from the second tubular intermediateoutput shaft 32′ is taken continuously from the carrier C2 and isselectively connected to the system output shaft 24 by means of alow-regime clutch L′.

The FIG. 2 variation has the advantage that when the low-regime clutchL′ is disengaged, the second epicyclic gear train E2′ is completelydisengaged from the system output shaft 24 (as opposed to the firstembodiment where the intermediate output shaft 32 is always engaged tothe system output shaft 24), whereby any problem arising from the secondepicyclic gear set during high-regime operation is not transmitted tothe system output shaft 24.

The invention is not restricted to the details of the foregoingembodiments. In particular, variators of types other than that describedcan be used. Moreover, the sizes of the gears may be varied to suit theparticular circumstances. For example, in the embodiments described, thesun gear S1 of the epicyclic gear train is the same size as the outputsun gear S2. However, instead of being the same sizes S1 maybe largerthan, or smaller than, S2 if appropriate.

1. A multi-regime, continuously variable ratio transmission system,comprising: coaxial system input and output shafts; a continuouslyvariable ratio transmission unit (variator) connected coaxially to thesystem input shaft and having a coaxial variator output shaft; and amixing epicyclic gear train having an input sun gear drivably connectedto the variator output shaft, a planet carrier drivably connected to thesystem input shaft and a first planet gear mounted on the planet carrierand drivingly engaged with the input sun gear; wherein the first planetgear drives a first intermediate output shaft which is arrangedcoaxially with the system input shaft and which is selectivelyconnectable to the system output shaft via a first clutch in ahigh-regime operation of the transmission operating from synchronousmode ratio to high forward ratio; and the first planet gear provides theinput for a second epicyclic gear train having an output which isselectively connectable to the system output shaft via a braking elementin a low-regime operation of the transmission operating from fullreverse ratio, through geared neutral to synchronous mode ratio.
 2. Atransmission system as claimed in claim 1, wherein the firstintermediate output shaft is provided with a sun gear which is driven bythe first planet gear of the mixing epicyclic gear train.
 3. Atransmission system as claimed in claim 2, wherein the sun gear on theoutput shaft is the same size as the input sun gear.
 4. A transmissionsystem as claimed in claim 1, wherein an axle of the planet gear of themixing epicyclic gear train carries a second planet gear which rotateswith the first planet gear and drives the first intermediate outputshaft.
 5. A transmission system as claimed in claim 4, wherein thesecond planet gear is the same size as the first planet gear.
 6. Atransmission system as claimed in claim 4, wherein the axle of the firstplanet gear of the mixing epicyclic gear train carries a third planetgear which rotates with the first planet gear and provides the input forthe second epicyclic gear train.
 7. A transmission system as claimed inclaim 1, wherein the second epicyclic gear train comprises a secondinput sun gear driven by the mixing epicyclic gear train, a planet geardriven by the second input sun gear and a planet carrier forming theoutput of the second epicyclic gear train.
 8. A transmission system asclaimed in claim 7, further comprising intermediate gearing connectingthe mixing epicyclic gear train and the second input sun gear.
 9. Atransmission system as claimed in claim 7, wherein the second epicyclicgear train comprises a second sun gear engaged with the planet gear ofthe second epicyclic gear train.
 10. A transmission system as claimed inclaim 9, further comprising means for selectively braking the second sungear.
 11. A transmission system as claimed in claim 10, wherein themeans for selectively braking comprises a clutch interposed between thesecond sun gear and a transmission system casing.
 12. A transmissionsystem as claimed in claim 11, wherein the sun gear is held stationarywith respect to the transmission casing and the means for selectivelybraking further comprises clutch means for selectively connecting theoutput of the second epicyclic gear train to the system output shaft.13. A transmission system as claimed in claim 2, wherein an axle of theplanet gear of the mixing epicyclic gear train carries a second planetgear which rotates with the first planet gear and drives the firstintermediate output shaft.
 14. A transmission system as claimed in claim3, wherein the axle of the first planet gear of the mixing epicyclicgear train carries the second planet gear which rotates with the firstplanet gear and drives the fast intermediate output shaft.
 15. Atransmission system as claimed in claim 5, wherein the axle of the firstplanet gear of the mixing epicyclic gear train carries a third planetgear which rotates with the first planet gear and provides the input forthe second epicyclic gear train.
 16. A transmission system as claimed inclaim 2, wherein the second epicyclic gear train comprises a secondinput sun gear driven by the mixing epicyclic gear train, a planet geardriven by the second input sun gear and a planet carrier forming theoutput of the second epicyclic gear train.
 17. A transmission system asclaimed in claim 3, wherein the second epicyclic gear train comprises asecond input sun gear driven by the mixing epicyclic gear train, aplanet gear driven by the second input sun gear and a planet carrierforming the output of the second epicyclic gear train.
 18. Atransmission system as claimed in claim 4, wherein the second epicyclicgear train comprises a second input sun gear driven by the mixingepicyclic gear train, a planet gear driven by the second input sun gearand a planet carrier forming the output of the second epicyclic geartrain.
 19. A transmission system as claimed in claim 5, wherein thesecond epicyclic gear train comprises a second input sun gear driven bythe mixing epicyclic gear train, a planet gear driven by the secondinput sun gear and a planer carrier forming the output of the secondepicyclic gear train.
 20. A transmission system as claimed in claim 6,wherein the second epicyclic gear train comprises a second input sungear driven by the mixing epicyclic gear train, a planet gear driven bythe second input sun gear and a planet carrier forming the output of thesecond epicyclic gear train.